The field of organic electronics is in a stage of explosive growth. Ten years ago there was a great deal of promise in optoelectronic devices based on organic materials and today they are a reality. Samsung is making 10 million Galaxy cell phones a month with organic LED displays. Samsung and LG are selling 55″, curved screen, high definition televisions, again composed solely of organic LEDs. Organic solar cells have been advanced to efficiencies exceeding amorphous silicon based devices and their current rate of increase will exceed thin film devices in five years and be competitive with crystalline silicon, the industry standard, on the horizon. Organic transistors have been used to fabricate backplanes for displays and are in line for applications such as flexible electronics and rf id tags. The use of organic materials opens the door to unparalleled versatility. The number of different organic materials that can be generated is limitless, suggesting that the device properties available with these materials and even the types devices themselves are going to be evolving and improving for some time to come.
Opto-electronic devices that make use of organic materials are becoming increasingly desirable for a number of reasons. Many of the materials used to make such devices are relatively inexpensive, so organic opto-electronic devices have the potential for cost advantages over inorganic devices. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on a flexible substrate. Examples of organic opto-electronic devices include organic light emitting devices (OLEDs), organic phototransistors, organic photovoltaic cells, and organic photodetectors. For OLEDs, the organic materials may have performance advantages over conventional materials. For example, the wavelength at which an organic emissive layer emits light may generally be readily tuned with appropriate dopants.
OLEDs make use of thin organic films that emit light when voltage is applied across the device. OLEDs are becoming an increasingly interesting technology for use in applications such as flat panel displays, illumination, and backlighting. Several OLED materials and configurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and 5,707,745, which are incorporated herein by reference in their entirety.
OLED devices are generally (but not always) intended to emit light through at least one of the electrodes, and one or more transparent electrodes may be useful in organic opto-electronic devices. For example, a transparent electrode material, such as indium tin oxide (ITO), may be used as the bottom electrode. A transparent top electrode, such as disclosed in U.S. Pat. Nos. 5,703,436 and 5,707,745, which are incorporated by reference in their entireties, may also be used. For a device intended to emit light only through the bottom electrode, the top electrode does not need to be transparent, and may be comprised of a thick and reflective metal layer having a high electrical conductivity. Similarly, for a device intended to emit light only through the top electrode, the bottom electrode may be opaque and/or reflective. Where an electrode does not need to be transparent, using a thicker layer may provide better conductivity, and using a reflective electrode may increase the amount of light emitted through the other electrode, by reflecting light back towards the transparent electrode. Fully transparent devices may also be fabricated, where both electrodes are transparent. Side emitting OLEDs may also be fabricated, and one or both electrodes may be opaque or reflective in such devices.
With all of the excitement around organic electronics and the promise their devices hold, it is surprising that the materials discovery methods are still largely rooted in age old serial methods of searching. Every new material starts with an idea, typically with a given device application in mind. The researcher could be thinking about an emitter in an OLED, an acceptor material in a solar cell or some other material for a particular device application. Whether the researcher gets an idea from a paper they read or they stare out the window, and idea pops into their head, the idea is a single molecule. This new “hypothetical” material is expected/hoped to have the properties that will make the device a winner. The next step is to try it out. They might put the molecule into a computer and see if the predicted electronic structure matches their expectation or they may go into the lab, synthesize the material and test the real thing. Either way, it is a serial process: one material is envisioned and tested. The researcher might look at a few variants, but the basic plan is to make it, examine it and test it in a device. This is the same process that has been used to identify all of the materials for many years. Altering this paradigm to foster a far more directed and productive path to new materials discovery would represent a significant advance in the art.
If the 20th century was the century of silicon, the 21st century will be all organic. The question is how to find the right material without spending the entire 21st century looking for it. Quite surprisingly, the present invention provides compositions and methods for facilitating the search for such material.